Russian authorities and militant websites say Aliaskhab Kebekov, the leader of the Caucasus Emirate insurgent group, has been killed in Daghestan.
The National Antiterrorism Committee (NAK) said on April 20 that Kebekov was one of three militants found dead after an armed confrontation between security forces and gunmen on the outskirts of Buinaksk, a city southwest of Daghestan's capital, Makhachkala.
Two websites associated with Islamic militants in Russia's North Caucasus -- kavkazcenter.com and jamaatshariat.com -- said Kebekov and two other men "became martyrs" in the town of Gerei-Avlak.
Kebekov, also known as Amir Ali Abu-Muhammad, was a Daghestani theologian who was chosen last year to succeed Doku Umarov as leader of the Caucasus Emirate, the main insurgent group in Russia's mostly Muslim North Caucasus.
The 43-year-old Kebekov, the first non-Chechen leader of Islamic insurgents in the post-Soviet North Caucasus, had a lower profile than Umarov, whose death was reported in March 2014 by a website close to the militants and later confirmed by Russian authorities.
The U.S. State Department designated Kebekov as a terrorist in March 2015, subjecting him to sanctions.
The insurgency stems from two post-Soviet separatist wars in Chechnya, adjacent to Daghestan.
Umarov proclaimed the territory of Russia's North Caucasus as the Caucasus Emirate ruled by Shari'a law in 2007.
Since then, the group has been blamed for a series of high-profile suicide attacks in Russia, including the bombing of Moscow's Domodedovo Airport in 2011 and a railway station in Volgograd in December 2013.
Canada, Russia, the United Kingdom, the United Nations, the United States, and the United Arab Emirates have designated the Caucasus Emirate as a terrorist organization.
In early 2009, Umarov announced the revival of a suicide attackers' unit called Riyad-us Saliheen Brigade of Martyrs.
The unit originally was established by Chechen field commander Shamil Basayev but temporarily stopped carrying out attacks after Basayev was killed in July 2006 in Ingushetia, a North Caucasus region adjacent to Chechnya.
In February 2014, Russian authorities launched unprecedented security measures for the Winter Olympics in Sochi after Umarov threatened that militants would attack the event.
However, the Sochi Olympics were conducted without terrorist violence.
The Caucasus Emirate's activities in the region have decreased in recent months amid reports that many prominent field commanders associated with the group have been traveling to Syria and Iraq to join Islamic State militants there.
The group's most recent major attack in the North Caucasus was in December 2014 in the Chechen capital, Grozny, when at least 14 police were killed and dozens wounded.
With reporting by Interfax and TASS